Multiplex signaling system



Sept. 18, 1934. l. G. WILSON MULTIPLEX SIGNALING SYSTEM Filed June 1,1933 Mai .33; i

W-q y E N N m0 R TS m M r VW A we 2 i VJ B ow 8 N w W q a R a FatentedSept. 18, 1934 2 Claims.

This invention relates to two-way signaling over a multiplicity ofcircuits such as those comprised in a'tel'ephone cable, although in itsbroadestaspects the invention is not limited to 5 telephony.

An object of the invention is to increase the message-carrying capacityof a cable or other group of transmission lines or circuits.

' I This object is accomplished according to the present invention bymultiplexing only certain of the lines of the cable for carriertransmission and pairing the message channelsthus formed with individuallines that are not multiplexed. A schematic circuit diagram of a cablesystem l5 embodying the invention is given in the single figure of theaccompanying drawing.

In the figure the cable is indicated by showing its two ends at 1, 1 thecentral portion through the major extent of its length being 120 brokenaway in the diagram.

Long cables of the prior art have generally consisted of voice frequencycircuits operated on a four-wire basis and loaded. That is, half thecircuits transmitted east and the other half transmitted west. Each linecontained one-way repeaters. A complete two-way voice circuit was madeup by associating as a two-way pair one one-way line with anothertransmitting in the opposite direction. Subscribers loops or othertwo-wire lines were then connected to the pair of one-way lines at eachterminal by means of hybrid repeating coils. This gave half as manytwo-way conversational circuits as there were pairs in the cable.

When an attempt is made to increase the message carrying capacity ofcable circuits by multiplexing the lines for carrier transmission, it isfound that cross-talk is a limitation and especially so if specialshielding or frequency alloca- 46 tion is not resorted to.

The invention provides an economical way of applying multiplex carrierto a cable of ordinary construction to increase the message-carryingcapacity. This is done by multiplexing certain of the lines, shown at10, 20 in the drawing, so

that they all transmit in the same direction, assumed eastward in thefigure. Since all of the channels on these lines transmit in the samedirection, the cross-talk requirements may be 50 brought withinpracticable limits without resorting to the use of separate cables orshields within the cable as might be necessary where oppositely directedlines were included within the cable and used the same frequency ranges.

, In the arrangement illustrated the same frequency ranges may be usedon carrier lines 16',

2O et'c., sothat the full economical operating range. of each line can,be utilized. Let it be supposed that a number, n, of such lines 10, 20etc. be multiplexed to provide m channels per line, or a total of mmchannels, all eastward. An equal number of westward channels is pro-,vided in the form of nm separate voice circuits 11, 12, '13, 14, etc.

At the west terminal, the carrier line 10 is associated with msubscribers lines L1, L2 to Lm by means of suitable carrier terminalapparatus such as modulators, 30, 31 etc. and band filters 40, 41 etc.in accordance with standard practice for carrier transmission. Each lineL1, L2 etc. has a hybrid coil H and line balancing network N forassociating the line with the carrier modulating circuit fortransmitting and with the return voice line 11 or 12 etc. for receiving.A similar arrangement is illustrated for associating the m lines L11,L12 to Llm with the carrier line 20 for transmitting eastward and withthe m individual voice lines 13, 14 etc. for receiving in the westwarddirection.

At the opposite cable terminal an entirely 39 similar arrangement isused. This is indicated for the group of lines L1, L2 to Lm' which areassociated with the multiplex line 10 at that terminal for eastwardtransmission and with the m individual lines of the cable 11, 12 etc. 5for a westward transmission. Suitable carrier receiving apparatuscomprising filters 40, 41' etc. and demodulators 50, 51 etc. are shownin the carrier receiving circuits that are branched from line 10. Asimilar arrangement is used for line 20.

Mid-line repeaters are shown in the carrier lines at RE and in the voicelines at RW. On account of the higher attenuation in the cara rier rangeit may be necessary to use closer repeater spacing in the carrier linesthan in the voice lines and this is indicated in the drawing by the twocarrier repeater points RE, RE for the one repeater point RW in thevoice lines.

The invention has application to many different situations in practice.Two such situations will be described.

In the first situation, it is assumed that a cable is to be laid, thatpresent requirements are for 40 voice circuits and that the expecteddemand will eventually increase to 90 voice circuits. (These figures areof course purely illustrative and an actual case might well involvefigures several times larger than these.)

use, multiplex carrier transmission is applied to the non=loadedcircuits and some of the voice' circuits have their repeaters reversedso that the voice lines may serve for opposite direction of transmissionand be paired with the carrier channel's. Eventually all 10 non-loadedlines will be multiplexed to provide9 channels each or a total of 9Geastward channels to go with the 90 Westward voice lines. The carrierlines may use the range of 4 to 40 KC or any other suitable range forthe 9 channels assumed.

In the second situation, let be assumed that a IOU-pair cable is alreadyin existence and consists only of loaded voice circuits, but that ademand has arisen for 40 additional conversational circuits. Instead ofgoing to the expense of laying an additional cable, 10 of the voicelines are equipped for carrier operation by removal of their loading andinstalling suitable terminal and repeater apparatus. On a 9 channelbasis these ten lines provide 90 one-way channels. The voice lines areall directed one way as in the other case above described and providethe 90 return circuits. 2

The carrier repeaters may be of the type disclosed in an application ofH. S. Black, Serial N0. 606,871, filed April 22, 1932;

The carrier lines arepreferably spaced apart' withinthe cable so that anumber of low frequency pairs intervene between carrier lines andprovide some shielding against cross-talk between the carrier lines.

What is claimed is:

1. Atwo-way signaling system comprising a cable consisting of aplurality of lines multiplexed for carrier transmission in the samedirection to provide a plurality of channels per line, and a number oflow frequency simplex one-way lines equal in number to the total numberof the carrier channels, and all transmitting in the oppositedirectionwith respect to said carrier channels, and two-way terminal circuitscooperating with said carrier and low frequency lines, each such two-wayterminal circuit being connected for eastward transmission over arespective carrier channel and for westward transmission over arespective lowfrequency line.

2. A two-Way telephone system comprising a cable consisting of nnon-loaded lines multiplexed for carrier operation to provide m carrieijtelephone channels per line all directed the same way and utilizing thesame over-all carrier frequency range, and n.m one-way loaded voicecircuits for transmission in the opposite direction, and terminalcircuit connections for utilizing each carrier channel as one side of afour-wire conversational circuit and one of said voice lines for theopposite side of the respective

